Powdered or particulate products often have to be transported from one place to another via pipes or ducting, and especially so within the factory or manufacturing plant where they are produced and/or packaged.
For example, milk powders may need to be transported, via pipes, from one part of a dairy factory to another, for example from a storage hopper to a packing room, where the milk powder may be packaged into bags. This often involves the milk powder having to travel significant distances, and in substantial volumes, through the pipes. The powder is usually transported through the pipes via vacuum-based transportation technologies.
The flow of powders through pipes or ducts are usually regulated or controlled by the use of shut-off valves, which are placed along the pipes at certain intervals. The valves, when open, allow for the continuous flow of powder along the pipes, and the valves, when closed, prevent or stop the flow of powder along the pipes, at the point where the valve is located.
One type of valve which may be used is a ball valve.
A ball valve is a form of quarter-turn valve which uses a hollow, perforated and pivoting ball (called a “floating ball”) to control the flow of powder through it. The valve is open when the aperture within the ball is in line with the flow, and the valve may be closed by rotating the ball 90-degrees by the use of a valve handle. The handle usually lies flat in alignment with the pipe (and flow) when the valve is open, but is perpendicular to the pipe when the valve is closed, making for easy visual confirmation of the valve's status.
Ball valves are generally durable, and usually perform well after many cycles, but primarily only when used with pipes that transport liquids or gases.
A disadvantage associated with the use of ball valves with pipes that are transporting powders (or any particulate material) is that when open, the powder can get stuck around the ball, and subsequently harden due to the flow pressure, and this may make it difficult to properly close the valve, and in some cases the valve may not be able to be properly closed at all.
Another disadvantage associated with ball valves is that the powder may interfere with the valve seat—which is usually in the form of a silicon or rubber bush, within which the ball sits, and against which the ball seals.
That is, powder can get between the ball and the valve seat which may prevent the valve from properly sealing. When this occurs, this may result in the transportation of the powder along the pipes being suspended whilst the valve is cleaned. This results in down time during the manufacturing and/or packaging process, which is clearly unsatisfactory. That is, having to suspend production whilst the valve is regularly cleaned results in lost production time, which therefore has cost and productivity implications.
When used in pipes for transporting milk powder, ball valves and/or the valve seats for same, usually need to be replaced approximately every month due to general wear and tear. Replacing ball valves, and/or the valve seats for same, can be a time-consuming and fiddly job.
Ball valves are also relatively expensive to purchase and install, as well as maintain.
Another type of valve which may be used is a butterfly valve.
A butterfly valve is a valve which utilises a closing mechanism in the form of a disc. Butterfly valves are generally favoured over ball valves because they are cheaper, and lighter in weight—meaning less support is required. The disc is positioned in the centre of the pipe, and passing through the disc is a rod connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel (open) or perpendicular (closed) to the longitudinal axis of the pipe and the direction of flow of powder through the pipe. When the valve is closed, the disc completely blocks off the pipe. When the disc is rotated a quarter turn, the valve is fully open.
Butterfly valves usually have a valve seat in the form of a silicon or rubber bush, which serves to seal the join between the two halves of the valve, as well as providing a seal between the edges of the rotatable disc and the valve seat, when the valve is closed.
A disadvantage associated with butterfly valves is that the abrasive nature of a powder, especially when transported under pressure, can degrade the unprotected valve seat over time, whereby it needs to be regularly replaced. That is, the valve seat needs to be replaced when it degrades to a point when the disc is not able to fully seal against the valve seat when the valve (disc) is closed.
When used in pipes for transporting milk powder, butterfly valves, and/or the valve seats for same, usually need to be replaced approximately every 2-3 weeks. This results in a significant amount of down time, and hence lost production time.
Moreover, for both ball valves and butterfly valves, the abrasive nature of a powder with respect to the valve seats means that parts of the valve seats can be “sand blasted” off, and hence fine particles of rubber or silicon may join the flow of powder and therefore contaminate the powder being transported. This is clearly unsatisfactory, and especially so for food powders such as flour and milk powder.
Perhaps in recognition of the above problems or difficulties there is available what is known as a deflected seat valve, an example being the TYCO SKI JUMP® valve, manufactured by Keystone International Inc. of the USA.
This valve has a profile like a ramp which deflects the abrasive powder over the valve seat, thereby reducing the wear and tear on the valve seat. However, a disadvantage associated with this valve is that is it relatively expensive to purchase, install and/or maintain. Furthermore, this valve only increases the life time of the valve seat to about 2-3 months. Moreover, this valve does not do away with the problem of fine particles of the rubber or silicon valve seat being “sand blasted” off and joining the flow of powder, and therefore contaminating same.